LTC6605-7 查看數據表（PDF） - Linear Technology

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LTC6605-7

Dual Matched 7MHz Filter with Low Noise, Low Distortion Differential Amplifier

Linear Technology 

LTC6605-7

APPLICATIONS INFORMATION

Functional Description

The LTC6605-7 is designed to make the implementation

of high frequency fully differential filtering functions very

easy. Two very low noise amplifiers are surrounded by

precision matched resistors and precision matched capaci-

tors enabling various filter functions to be implemented by

hard wiring pins. The amplifiers are wide band, low noise

and low distortion fully differential amplifiers with accurate

output phase balancing. They are optimized for driving

low voltage, single-supply, differential input analog-to-

digital converters (ADCs). The LTC6605-7 operates with

a supply voltage as low as 2.7V and accepts inputs up to

325mV below the V– power rail, which makes it ideal for

converting ground referenced, single-ended signals into

differential signals that are referenced to the user-supplied

common mode voltage. This is ideal for driving low volt-

age, single-supply, differential input ADCs. The balanced

differential nature of the amplifier and matched surround-

ing components provide even-order harmonic distortion

cancellation, and low susceptibility to common mode noise

(like power supply noise). The LTC6605-7 can be operated

with a single-ended input and differential output, or with

a differential input and differential output.

The outputs of the LTC6605-7 can swing rail-to-rail. They

can source or sink a transient 70mA of current. Load

capacitances should be decoupled with at least 25Ω of

series resistance from each output.

Filter Frequency Response and Gain Adjustment

Figure 3 shows the filter architecture. The Laplace transfer

function can be expressed in the form of the following

generalized equation for a 2nd order lowpass filter:

( ) VOUT(DIFF)

VIN(D IF F )

GAIN

=

1+ s +

2πfO • Q

s2

2πfO

2

,

with GAIN, fO and Q as given in Figure 3.

Note that GAIN and Q of the filter are based on component

ratios, which both match and track extremely well over

temperature. The corner frequency fO of the filter is a

function of an RC product. This RC product is trimmed to

±1% and is not expected to drift by more than ±1% from

nominal over the entire temperature range –40°C to 85°C.

As a result, fully differential filters with tight magnitude,

phase tolerance and repeatability are achieved.

Various values for resistors R1 and R4 can be formed

by pin-strapping the internal 100Ω and 400Ω resis-

tors, and optionally by including one or more external

resistors. Note that non-zero source resistance should be

combined with, and included in, R1.

R1

+

VIN(DIFF)

R1

–

R2

400Ω

R3

125Ω

R4A

REXT

R4B R3

125Ω

R2

400Ω

C2

114.8pF

C1

69.3pF

+–

–+

–

VOUT(DIFF)

+

C1

69.3pF

C2

114.8pF

R4 = R4A + R4B + REXT

Figure 3. Filter Architecture and Equations

10

66057 F03

66057f

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